Dvc: import: support --no-exec

[jorgeorpinel]

What's the point of import-url --no-exec?

Our docs read "E.g. if the file or directory already exist it can be used to skip download. dvc commit .dvc should be used to calculate the URL and data hash, update the .dvc files, and save existing data to the cache."

Why would you want to import a file that you already have, and that would the be immediately overwritten as a regular output with commit? (if I get that last part right)

And why doesn't it exist in import?

[jorgeorpinel]

Please transfer to dvc.org if this is mainly a matter of re-explaining the option's motivation. But it seems inconsistent that import doesn't also have it so we could keep this one as a request to add it there.

[skshetry]

@jorgeorpinel, a contributor asked for it, here's the motivation: #3513.

[jorgeorpinel]

I see. Shouldn't it be in import as well though? For consistency at least, and because of the same motivation.

Also commented in https://github.com/iterative/dvc/issues/3513#issuecomment-692192135

[efiop]

@jorgeorpinel We'll add one if someone will ask for it. The consistency there is not as obvious to add a feature that is uncalled for.

[jorgeorpinel]

I'm mentioning all this because someone asked for it implicitly in https://discuss.dvc.org/t/direct-copy-between-shared-cache-and-external-dependencies-outputs/487/3

[efiop]

@jorgeorpinel Ah, ok, makes sense. Repurposing this issue then.

[jorgeorpinel]

Thanks!

[BurnzZ]

Hello everyone! I'm picking this up. :)